Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
  • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
  • C12N9/96—Stabilising an enzyme by forming an adduct or a composition; Forming enzyme conjugates
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K47/00—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
  • A61K47/06—Organic compounds, e.g. natural or synthetic hydrocarbons, polyolefins, mineral oil, petrolatum or ozokerite
  • A61K47/08—Organic compounds, e.g. natural or synthetic hydrocarbons, polyolefins, mineral oil, petrolatum or ozokerite containing oxygen, e.g. ethers, acetals, ketones, quinones, aldehydes, peroxides
  • A61K47/10—Alcohols; Phenols; Salts thereof, e.g. glycerol; Polyethylene glycols [PEG]; Poloxamers; PEG/POE alkyl ethers
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K47/00—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
  • A61K47/06—Organic compounds, e.g. natural or synthetic hydrocarbons, polyolefins, mineral oil, petrolatum or ozokerite
  • A61K47/16—Organic compounds, e.g. natural or synthetic hydrocarbons, polyolefins, mineral oil, petrolatum or ozokerite containing nitrogen, e.g. nitro-, nitroso-, azo-compounds, nitriles, cyanates
  • A61K47/18—Amines; Amides; Ureas; Quaternary ammonium compounds; Amino acids; Oligopeptides having up to five amino acids
  • A61K47/183—Amino acids, e.g. glycine, EDTA or aspartame
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K47/00—Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
  • A61K47/06—Organic compounds, e.g. natural or synthetic hydrocarbons, polyolefins, mineral oil, petrolatum or ozokerite
  • A61K47/26—Carbohydrates, e.g. sugar alcohols, amino sugars, nucleic acids, mono-, di- or oligo-saccharides; Derivatives thereof, e.g. polysorbates, sorbitan fatty acid esters or glycyrrhizin
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P37/00—Drugs for immunological or allergic disorders
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
  • Y02A50/30—Against vector-borne diseases, e.g. mosquito-borne, fly-borne, tick-borne or waterborne diseases whose impact is exacerbated by climate change

Definitions

• This invention relates to stable aqueous systems comprising proteins.
• Background of the Invention The loss of a protein's native tertiary structure is generally associated with the loss of its biological activity. It is therefore crucial to ensure that an active protein (e.g. vaccine, therapeutic protein, diagnostic protein etc.) is stored under conditions where the native tertiary structure is maiptained.
• an active protein e.g. vaccine, therapeutic protein, diagnostic protein etc.
• Proteins are macromolecules consisting of sequences of 20 different naturally occurring amino acids. Seven of these amino acids (aspartic acid, glutamic acid, histidine, cysteine, tyrosine, lysine and arginine) contain a side-chain capable of engaging in acid-base equilibria. This means that they can either accept or donate a proton depending on pH and other species present in the solution. Serine and threonine are also capable of exchanging protons with the surrounding molecules.
• EP0513914 discloses the stabilisation of uricase with aspartic acid at a concentration of 750 mM.
• US3051627 discloses chymotrypsin in water with an amino acid, at pH 4.
• an aqueous system comprises a protein and one or more stabilising agents, characterised in that
• the one or more stabilising agents have ionisable groups capable of exchanging protons with the protein and with the ionised products of water dissociation;
• the ionisable groups include first groups that are positively charged when protonated and uncharged when deprotonated, and second groups that are uncharged when protonated and negatively charged when deprotonated;
• an aqueous system comprises, a protein and one or more stabilising agents, characterised in that
• the one or more stabilising agents have ionisable groups capable of exchanging protons with the protein and with the ionised products of water dissociation;
• a composition comprises a protein and one or more stabilising agents as defined above, adsorbed on a solid.
• the present invention also provides a method of identifying an appropriate pH to optimise the storage stability of a protein in aqueous environment, comprising determining a pH with a value in the range 4 to 9 at or near a value at which the protein is in a proton-exchange equilibrium state with respect to its surroundings that is optimised for storage stability, i.e. in a condition of optimum proton-exchange equilibrium.
• the optimum proton-exchange equilibrium state exists at a pH at which the following two conditions are met: a) the probability of protonation (P) of each individual amino acid in the protein sequence (as defined by the pK a of each individual amino acid) is as far away as possible from 50% (i.e. 50% in protonated form and 50% in deprotonated form); and b) the overall protonation of all amino acids in the protein sequence (as defined by pK a values of all amino acids in the sequence) is as high as possible.
• the optimum proton-exchange equilibrium state i.e. the state at which storage stability is optimised, is that in which conditions a) and b) are both met as far as possible, with a compromise being reached between the two conditions for overall optimisation.
• condition a) requires a knowledge of the amino acid sequence of the protein (this may be based on all amino acids, but is preferably based on only those amino acids accessible at the surface of the protein in folded, active condition) and the pKg values of the amino acid side-chains of the protein. Only the 7 protonatable amino acids are of relevance.
• condition b) also requires a knowledge of the isoelectric point of the protein. In this way, the pH at which conditions a) and b) are both met as far as possible can be determined.
• the probability of protonation (P), which is also referred to herein as the proton exchange frequency, at any pH can be calculated as described above and plotted against pH to enable determination of the pH (in the interval 4 to 9) at which P is at a minimum (P minimum)-
• the probability of protonation (P) can be calculated by the following mathematical function:
• M is the relative molecular weight of the protein unit
• N is the number of the given amino acid side-chains in the protein unit; and pK a is the negative of the logarithm of the acid dissociation constant K 3 of the given amino acid side-chain.
• Adjustment to take account of condition b) can then be made by calculating an optimised value of P (P op t i m i se d) by the following equation:
• the pH value corresponding to P op timised that is lower than the pH value corresponding to that of P m i n i m um can then be determined, giving the calculated optimum pH for the protein.
• references to pH being "at or near” a value usually mean within ⁇ 0.5 pH units, preferably ⁇ 0.4 pH units, more preferably ⁇ 0.2 pH units.
• Data for isoelectric point values and amino acid sequences, including accessibility at the surface of amino acids in the protein in folded, active condition, for many proteins is readily available from various sources, with one convenient source for sequence data being the Protein Data Bank information databank which is available on-line at www.rcsb.org/pdb. Other, paper-based sources of information are also available.
• the invention also provides a method of treating a protein in aqueous environment in initial conditions of non-optimum storage stability to make the storage stability closer to optimum, comprising adjusting the pH to a value in the range 4 to 9 at or near a value at which the protein is in a proton-exchange equilibrium state with respect to its surroundings that is optimised for storage stability.
• the invention additionally provides a method of providing a protein in aqueous environment with optimised conditions for storage stability, comprising providing a pH in the range 4 to 9 at or near a value at which the protein is in a proton-exchange equilibrium state with respect to it surroundings that is optimised for storage stability.
• the invention also includes within its scope a protein in aqueous environment at a pH in the range 4 to 9 at or near a value at which the protein is in a proton- exchange equilibrium state with respect to its surroundings that is optimised for storage stability.
• the stabilised protein may be in a microbiologically sterile form, and is conveniently contained or stored in a sealed, sterile container such as a vial, syringe or capsule.
• the invention also provides a method of storage of a protein in aqueous environment, including at ambient temperature and above, comprising providing the environment with a pH in the range 4 to 9 at or near a value at which the protein is in a proton-exchange equilibrium state with respect to its surroundings that is optimised for storage stability.
• a further aspect of the invention is a method of selection of conditions capable of protecting a protein in aqueous environment against heat degradation (including at ambient temperature or above), comprising selecting a pH in the range 4 to 9 at or near a value at which the protein is in a proton-exchange equilibrium state with respect to its surroundings that is optimised for storage stability.
• a protein at a suitable pH at or near (usually within 0.5 pH units, preferably within 0.4 pH units and more preferably within 0.2 pH units) a value at which the proton exchange equilibrium state with respect to its surroundings is optimised for storage stability, so the storage stability of the protein (either at ambient temperature (about 20 0 C) or at elevated temperature) can be increased, possibly substantially, compared with the storage stability of the protein in non-optimised condition (usually at pH 7).
• references to optimising storage stability of a protein mean moving towards the optimum, without necessarily achieving the optimum. By bringing storage stability closer to optimum, so storage stability is improved as compared with non-optimum conditions, e.g. at pH 7.
• Storage stability can generally be further enhanced by use of one or more additives including one or more species capable of exchanging protons with the protein with less extreme pK a values than those of H 3 O + (which has a pK a of 13.99) and OH ' (which has a pK a of -1.74). It is preferred to use one or more additives with first and second functional groups as discussed above.
• Additives are suitably present in an amount such that the total concentration of additives is in the range 1 mM to 1 M, preferably 1 mM to 200 mM, most preferably 5 mM to 100 mM. Good results have been obtained with low levels of additives (around 5 mM) with certain proteins, with little benefit being obtained by using higher levels, although exceptions have been found, e.g. with catalase where higher levels of additives (100 mM) gave significantly better stability than lower levels (10 mM). In certain practical applications, especially in medical applications, it will often be desirable to use as low concentrations of additives as possible. Discoveries underlying the present invention have a theoretical basis, as discussed herein, which have been borne out in practice.
• this specification describes how a stabilising system for any protein can be determined, based on available information. Nevertheless, the benefits of the invention may also be achieved on an empirical basis, on the understanding that, for any protein in solution, and depending on the presence of other additives, there is a relationship between stabilisity and pH, and that there is a ph at which the protein has optimum stability. Based on the information presented herein, one of ordinary skill in the art can readily determine additives that are likely to be useful and then whether they in fact meet the criteria by which the invention is defined. It appears that, prior to the present invention, the significance of proton exchange and hence pH in relation to the storage stability of proteins has not been appreciated.
• the present invention enables improvements to be made in the storage stability of proteins by selecting an appropriate pH, preferably in combination with one or more additives.
• the invention thus enables improvements to be made in the storage stability of proteins in aqueous environment such that proteins can be stored for extended periods of time at ambient temperatures without significant loss of activity, thus avoiding the need for freezing or refrigeration. While most of the experimental examples herein use elevated temperatures (typically between 55 0 C and 65°C) to accelerate loss of activity, the results provide a very good indication of protein stability at lower, including ambient, temperatures.
• the invention is applicable to a wide range of proteins, including polypeptides etc. as discussed above, including protein vaccines and therapeutic proteins, and including relatively small proteins/polypeptides such as glucagon (relative molecular weight 3550) and insulin (relative molecular weight 6000).
• a further aspect of the present invention is a composition
• a composition comprising a protein and one or more additives adsorbed on an adjucant.
• the or each additive is selected as if present in aqueous solution, as defined above (but is not necessarily water- soluble).
• Such a composition may be obtained by adsorption, onto an adjuvant, of the components from an aqueous composition or the invention.
• Description of the Drawings Figure 1 is a graph of % protonated/de-protonated form versus pH for the
• Figure 2 is a graph of the product of the normalised concentration of the protonated form [HA] and the deprotonated form [A] in arbitrary units versus pH for the 7 protonatable amino acids;
• Figure 3 is a graph of proton exchange frequency (relative to the size of protein) in arbitrary units versus pH for the enzyme papain, illustrating the relative rate of proton exchanges on the surface of the papain molecule;
• Figure 4 is a graph of % protonation of the amino acid side-chains of glucose oxidase and papain versus pH;
• Figure 5 is a pair of graphs of proton exchange frequency (relative to size of protein) in arbitrary units versus pH for glucose oxidase and horseradish peroxidase, showing the difference between the theoretical pH optimum for protein stability calculated on the basis of the minimum overall proton exchange frequency and the actual pH optimum;
• Figure 6 is a graph of concentration (in ⁇ M) versus pH for H 3 O + and OH ' in aqueous solution at 25 0 C
• Figure 7 is a graph of proton exchange frequency (relative to the size of protein) in arbitrary units P versus pH, illustrating estimation of pH optimum for protein stability based on known amino acid sequence and isoelectric point of a protein;
• Figure 8 is a graph similar to Figure 3, illustrating estimation of pH optimum for stability of glucose oxidase based on known amino acid sequence and isoelectric point of the protein;
• Figure 9 is a graph similar to Figure 8, for catalase;
• Figure 10 is a graph similar to Figure 8, for papain;
• Figure 11 is a graph similar to Figure 8, for glutamate dehydrogenase;
• Figure 12 is a graph of activity recovery of uricase activity on incubation at
• this invention relates to the stability of proteins, particularly the stability of proteins in an aqueous environment, e.g. in aqueous solution, in aqueous gel form and in solid state (or other non-liquid state) where free or bound water is present, and concerns the storage stability of proteins, i.e. stability with time, including stability at ambient temperatures (about 20°C) and above.
• protein is used herein to encompass molecules or molecular complexes consisting of a single polypeptide, molecules or molecular complexes comprising two or more polypeptides and molecules or molecular complexes comprising one or more polypeptides together with one or more non-polypeptide moieties such as prosthetic groups, cofactors etc.
• polypeptide is intended to encompass polypeptides comprising covalently linked non-amino acid moieties such as glycosylated polypeptides, lipoproteins etc.
• the invention relates to molecules having one or more biological activities of interest which activity or activities are critically dependent on retention of a particular or native three-dimensional structure in at least a critical portion of the molecule or molecular complex.
• the invention may be applicable to polypeptides having a molecular weight of at least 2000 (i.e. consisting of at least about 15 amino acids) where at least basic motifs of secondary or tertiary structure possibly important for protein function might be formed.
• the invention is applicable to any system in which the retention of structural characteristics of a protein, in particular the secondary, tertiary and quaternary structure, and the retention of functional characteristics of the protein, in particular the enzyme activity, antigen binding, receptor binding, ligand binding or other specific binding events, are of importance.
• the application of the invention reduces significantly the probability of irreversible conformational change and irreversible aggregation of a protein and consequent loss of protein activity.
• the invention is applicable to stabilisation of a protein throughout its product life including isolation or expression, purification, transport and storage.
• the invention is applicable to polypeptides with a relative molecular weight of at least 2000 where at least basic motifs of secondary or tertiary structure are likely to be formed. There is no upper limit of the relative molecular weight that would limit application of the present invention.
• the invention is applicable to proteins containing any proportion of alpha helix, beta sheet and random coil.
• the invention is applicable both to globular proteins and to fibrillar proteins.
• the invention is applicable to proteins whose tertiary structure is maintained solely by means of non-covalent interactions as well as proteins whose tertiary structure is maintained by combination of non-covalent interactions and one or more disulphide bridges.
• the invention is applicable to monomeric proteins as well as proteins consisting of two, three, four or more subunits.
• the invention is also applicable to protein conjugates.
• the invention is applicable to proteins that do not contain any non-peptide components as well as glycoproteins, lipoproteins, nucleoproteins, metalloproteins and other protein containing complexes where protein represents at least 10% of the total mass. It is applicable to proteins that do not require a cofactor for their function as well as to proteins that require a coenzyme, prosthetic group or an activator for their function.
• the invention is applicable to proteins dissolved freely in aqueous solutions, or present in an aqueous system as a dispersion or suspension, as well as proteins attached to solid substrates such as vaccine adjuvant or cellular membrane by means of hydrophobic, ionic or ligand exchange interactions.
• the invention is also applicable to proteins dissolved in aqueous gel form and proteins in solid state where water has been removed partially or fully from an aqueous solution by drying or by freeze-drying where free or bound water is still present.
• the protein may be native or recombinant, glycosylated or non-glycosylated, autolytic or non-autolytic.
• the invention is particularly applicable to the following groups of proteins. Protein or peptide hormones and growth factors
• protein or peptide hormones and growth factors depends on their ability to bind to a specific receptor. Such binding event is linked closely to the protein conformation.
• the retention of three-dimensional structure of the protein, or at least the 3-D structure of key domains, is therefore crucial for their function.
• the retention of structural and functional characteristics is also of paramount importance for the regulatory approval of the protein therapeutics.
• therapeutic protein or peptide hormones include: ⁇
• Insulin treatment of diabetes
• Glucagon treatment of diabetes
• Granulocyte colony stimulation factor (used as part of chemotherapy) Therapeutic enzymes
• therapeutic protein or peptide hormones include:
• Streptokinase thrombolytic agent in treatment of ischemic stroke
• the immunogenic activity of protein vaccines depends (to a large extent) on the structural integrity of the key protein antigens, especially in relation to conformational epitopes (where antibodies are required to bind disparate regions of the polypeptide chain broght together by native folding). Irreversible conformational changes and irreversible aggregation lead to- inactivation of vaccines.
• the same considerations apply to proteins adsorbed onto particles, such as alumina particles, or other (non-particulate) surfaces when substantial regions of each protein molecule are still in full interaction with solvent water. This is of particular importance in vaccine distribution in the third world where the maintenance of the cold chain is very difficult or impossible, partly through practical or logistic limitations and partly through cost.
• the present invention can be applied to recombinant protein vaccines as well as attenuated viruses or whole cell vaccines, providing the key antigens consist of polypeptide chains.
• vaccines include: Hepatitis B vaccine Malaria vaccine Human papilloma vaccine
• therapeutic antibodies are based on their specific interactions with target antigens. So, in order to maintain their function, the retention of the three- dimensional structure is essential for the duration of their shelf life. Although generally very stable at ambient temperature, due to the inherent rigid, stable structure of the immunoglobulin fold or domain, antibodies can benefit from the present invention, by further increasing their stability in storage.
• therapeutic antibodies that can be used, for example, in cancer therapy include: anti-Epidermal Growth Factor Receptor (EGFR) monoclonal antibody anti-HER2 monoclonal antibody (breast cancer therapy) anti-CD52 monoclonal antibody (chronic lymphocytic leukaemia therapy) anti CD20 monoclonal antibody (aggressive lymphoma therapy) Interferons
• Interferons are rather unstable polypeptides of therapeutic importance, that are used, for example, in multiple sclerosis therapy.
• Application of the present invention can increase the shelf life and cost effectiveness of interferons.
• Interferon beta is the main current example.
• Other therapeutic proteins are rather unstable polypeptides of therapeutic importance, that are used, for example, in multiple sclerosis therapy.
• Application of the present invention can increase the shelf life and cost effectiveness of interferons.
• Interferon beta is the main current example.
• Other therapeutic proteins are rather unstable polypeptides of therapeutic importance, that are used, for example, in multiple sclerosis therapy.
• Application of the present invention can increase the shelf life and cost effectiveness of interferons.
• Interferon beta is the main current example.
• Other therapeutic proteins are rather unstable polypeptides of therapeutic importance, that are used, for example, in multiple sclerosis therapy.
• Application of the present invention can increase the shelf life and cost effectiveness of interferons.
• Interferon beta is the main current example.
• Erythropoietin (stimulating erythrocyte production)
• Darbepoietin alpha (stimulating erythrocyte production)
• Blood coaguation factors mainly Factor VIII and Factor IX (treatment and control of haemophilia)
• Immunosuppressive agents treatment of various conditions such as asthma, allergic rhinitis or multiple sclerosis
• Human albumin Protein C (antithrombic agent)
• diagnostic proteins particularly enzymes and antibodies.
• in-kit reference standards of the analytes through which the assay is calibrated and subjected to QC, must be rigorously stabilised, as any drift in their integrity will cause a resultant drift in accuracy of the whole kit. Impaired activity can lead to false results or poor performance (e.g. slow running of the procedure). Stability of the functional activity of diagnostic proteins throughout their product life is therefore of paramount importance. Manufacturers of diagnostic products are keen to find approaches and formulations that would eliminate costly lyophilisation, which causes substantial processing bottlenecks. Examples of diagnostic proteins include:
• Oxidases such as glucose oxidase, galactose oxidase, cholesterol oxidase
• Dehydrogenases such as glutamate dehydrogenase, glucose dehydrogenase lsomerases such as invertase
• Hydrolases such as trypsin, or chymotrypsin
• Integral assay reference standards supplied in kit form such as hormones, growth factors, microbial proteins, metabolic proteins, soluible forms of structural proteins etc.
• industrial proteins include:
• Reference standards of therapeutic or diagnostic proteins are of great importance for standardisation of therapeutic and diagnostic procedures.
• the stability of reference standards is of fundamental importance.
• a wide range of protein-based reference standards are therefore an ideal target for the present invention.
• the protein used in the invention can be maintained substabtially in its native state.
• native protein is used to describe a protein having retained tertiary structure, and distinction from proteins that have undergone a degree of unfolding or denaturation.
• a native protein may incorporate some chemical modification, e.g. deamidation, rather than physical modification.
• the present stabilisation technology can be applied to stabilising proteins adsorbed on solid surfaces such as alumina.
• solid surfaces such as alumina.
• phosphate is a preferred stabilising agent. It appears that phosphate may provide additional desirable properties, e.g. when formulations contain phosphate anion (> 20 mM). The reasons behind the importance of phosphate are not entirely clear, but it is believed that phosphate anion plays a role in appropriate binding of the vaccine onto alumina (see, for example, Iyer S. et al.: Vaccine 22 (2004) 1475-1479).
• the present invention is based at least in part on the realisation that each exchange of proton in the energetically favourable acid -base direction is accompanied by a release of energy proportional to the difference in pK a between the amino acid side-chain and the molecule with which the proton is exchanged.
• the energy of such transfer will be dissipated into the surrounding environment in the form of enthalpy (heat release) and change in entropy. This can lead to a temporary change of the structural and energetic characteristics in the vicinity of the amino acid involved. Although it cannot be ruled out that such event might even result in breakage of chemical bond, the possibility of such effect is undoubtedly very small.
• Protein stability can be enhanced by minimising the frequency of the proton exchanges at its surface.
• protein stability can be enhanced by keeping as high a proportion of the side-chains as possible in the protonated form.
• the pKa of a compound is an indication of its acid-base behaviour. The value varies with temperature, and it should be noted that the pKa value of an amino acid side-chain is not necessarily the same as that of the free amino acid (although the difference should not be too great).
• the rate of the protonation/de-protonation cycle is reduced by the low proportion of either the protonated form (at high pH) or the de-protonated form (at low pH).
• the maximal proton exchange frequency will occur at pH around 4.15, in the case of histidine around pH 6 etc.
• the relative rate of the proton exchanges of the seven amino acids is shown as a function of pH in Fig. 2.
• the relative rate is expressed as the product of the concentrations of the protonated (HA) and the de-protonated (A) form of the amino acid side-chain, with total non- dimensional concentration of the amino acid side-chain arbitrarily selected as 1.
• the protein stability can be enhanced by minimising the overall frequency of the proton exchanges, i.e. the sum of all proton exchange events at the protein surface.
• An example of the overall frequency of proton exchange frequency is shown in Fig. 3 for the protease enzyme papain. This was calculated by summing the proton exchange frequencies of the individual amino acids (as shown in Fig. 2) while the relative contribution of each amino acid was determined by its the relative abundance in the papain sequence.
• the pH optimum for papain stability was found experimentally to be between 5.8 and 6.2. This corresponds approximately to the minimum of the proton exchange rate (Fig. 3).
• the relative frequency of the proton exchange is only one of the contributing factors to the protein stability/instability and has to be considered in the context of other contributing factors (see below). This means that, whilst the frequency of the proton exchange is a good indication of the pH optimum, the highest stability is not necessarily attained precisely in the minimum of the proton exchange frequency profile. This is demonstrated in some of the Examples, below. Minimising free (Gibbs) energy of the side-chains
• the Gibbs free energy of all protonatable amino acid side-chains is lower in the protonated form than in the de-protonated form. This is because the free electron pairs (onto which the proton binds) are lower in energy in the presence of the proton compared with its absence. Binding of protons onto the amino acid side-chains thus decreases overall free energy of the entire protein.
• the protein stability can therefore be enhanced by maximising the protonation of the amino acids on its surface. The percentage of overall protonation at the surface of two model proteins
• the amount of energy released during the proton exchanges depends on the difference in pK a between the species involved. It is therefore beneficial for the stability of the protein to minimise the impact of continuous interactions with compounds of extreme pK a (especially those involving H 3 O + and OH ' ) and ensure that these are replaced by interactions with compounds with less extreme pK a values.
• the dominant species with "extreme pK a * values" in aqueous solutions are H 3 O + and OH ' . The more extreme is the pK a value of a species, the less likely it is that this species occurs in the "high energy" form (i.e.
• the energy impact of the proton exchanges between the amino acid side- chains and H 3 O + or OH " is indicated in Table 1.
• the impact is expressed as the difference in pK a between the colliding species (the difference in pKg being proportional to the energy released during the collision).
• the pH adjustment is not the only measure that can be taken to improve the protein stability.
• the stability can be further improved by adding compounds that can engage in "mild” proton exchanges with the amino acid side-chains of the protein and thus reduce further the probability of the destructive "energetic” proton exchanges with H 3 O + or OH " .
• the first functional group has a pK a at least one unit higher than the pH optimum and is positively charged at the pH optimum. This means that the charge of the group switches from neutral to positive while accepting the proton (e.g. amino group, purine, TRIS etc.).
• the second functional group preferably has a pK a at least one unit lower than the pH optimum and is negatively charged at the pH optimum. This means that the charge of the group switches from negative to neutral while accepting the proton (e.g. carboxylic group).
• a small amount of buffer can be used alongside the additives in order to maintain the optimal pH.
• the incorporation of the additives can affect slightly the pH optimum for the protein stability (within approximately 0.5 pH unit depending on the nature and quantity of the additives).
• Step 1 (this can be done easily in MS-Excel) Calculate the proton exchange frequency function (P) and plot against pH: where
• M is the relative molecular weight of the protein unit
• [HA] is the proportion of the protonated form of the amino acid at the given pH. 0 ⁇ [HA] ⁇ 1.
• [A] is the proportion of the de-protonated form of the amino acid at the given pH. 0 ⁇ [A] ⁇ 1.
• the first functional group has a pK a higher than the pH optimum for the protein stability (as estimated in steps 1 and 2) and is positively charged at the pH optimum. This means that the charge of the group switches from neutral to positive while accepting the proton.
• the pK a of the functional group must be higher than the pH optimum for the protein stability. Preferably, it should be within 5 pH units above the pH optimum. More preferably, it should be within 0.5 - 4 pH units above the pH optimum. Most preferably, it should be within 1 - 3 pH units above the pH optimum for the enzyme.
• Functional group 2 :
• the second functional group has a pK a at least one unit lower than the pH optimum for the protein stability (as estimated in steps 1 and 2) and is negatively charged at the pH optimum. This means that the charge of the group switches from negative to neutral while accepting the proton (e.g. carboxylic group).
• the pK a of the functional group must be lower than the pH optimum for the protein stability. Preferably, it should be within 5 pH units below the pH optimum. More preferably, it should be within 0.5 - 4 pH units above the pH optimum. Most preferably, it should be within 1 - 3 pH units below the pH optimum for the enzyme.
• the formulation can only contain the first functional group (i.e. the positively charged one).
• the formulation contains both the first and the second functional group.
• the two functional groups can be contained within one compound (e.g. an amino acid).
• the two functional groups are located on more than one additive (e.g. one additive contains the first, negatively charged group, and the other additive contains the second, positively charged group).
• one additive contains the first, negatively charged group, and the other additive contains the second, positively charged group.
• the buffering ability of the additives can be sufficient in those cases where their pK a is only about 1 pH unit from the pH optimum. If the pK a is further away their buffering ability may be reduced. A small concentration of buffer with pK a close to the pH optimum can then be used in order to maintain the required pH.
• the invention can be combined with other well established approaches to protein stability.
• a protease inhibitor can be incorporated in the formulation to ensure that the protein is not slowly digested by protease activity present in the sample.
• Another additive that may be used is a polyalcohol, e.g. at a concentration of at least 0.5%, and typically up to 5% (w/w).
• a polyalcohol e.g. at a concentration of at least 0.5%, and typically up to 5% (w/w).
• saccharides such as inositol, lactitol, mannitol, xylitol and trehalose.
• the ionic strength of the protein formulation stabilised by application of the present invention can be adjusted to meet the requirement for the intended use of the formulation (e.g. isotonic formulation for therapeutic use).
• experiments showed repeatedly that in principle the stability of proteins at room temperature mirrors that at higher temperature, the rate of activity decline being many orders of magnitude slower at room temperature compared with that at increased temperature (e.g. 6O 0 C).
• Catalase from bovine liver, Sigma C9322, 2380 U /mg solid
• Citric acid (Fisher, Code C/6200/53)
• Lactoperoxidase from bovine milk, DMV International: 1 ,050 units mg '1 by ABTS method pH 5.0
• Lysine (Sigma, Code L5501) Methanol (Fisher, Code M/3950/17)
• TRIS base - Tris(hydroxymethyl)aminomethane (Fisher Bioreagents, CodeBPE152-1)
• phosphate buffers of given concentration and pH (X mM, pH Y) used in this work were prepared by mixing disodium hydrogen orthophosphate (X mM) with sodium dihydrogen orthophosphate (X mM) to achieve the required pH Y.
• citrate/phosphate buffers of given concentration and pH (X mM, pH Y) used in this work were prepared by mixing di-sodium hydrogen orthophosphate (X mM) with citric acid (X mM) to achieve the required pH Y.
• an aqueous solution of a given enzyme was prepared with selected additives in an Eppendorf tube. Unless stated otherwise, the concentrations of enzymes used were as follows:
• Glucose oxidase 350 ⁇ g /mL
• Lactoperoxidase 100 ⁇ g /ml_
• Horseradish peroxidase 10 ⁇ g /ml_
• the Examples may include information on the particular enzyme, procedure to select optimum conditions for stability (using the algorithm described above) based on surface amino acids, and practical examples demonstrating the stability of the enzyme at increased temperature. All amino acid sequences were obtained from the publicly available Protein Data Bank (http://www.rcsb.org/pdb).
• Glucose oxidase (from Penicillium sp.) consists of two identical subunits (M r of each approx. 80,000). The isoelectric point of glucose oxidase as approximately 4.3. The abundance of the acid-base amino acids in each subunit is shown in Table 4. Table 4
• the first number indicates the number of cysteines that are not engaged in disulphide bond.
• the number in brackets indicates the total number of cysteines in the subunit.
• the proton exchange frequency profile for glucose oxidase is shown in Fig. 8.
• the pH optimisation algorithm gives the following results for glucose oxidase:
• the phosphate buffer was prepared by mixing di-sodium hydrogen orthophosphate (50 mM) and sodium dihydrogen orthophosphate (50 mM) to achieve the required pH. There was no measurable activity following incubation of glucose oxidase at 60 0 C for 15 minutes in the presence of phosphate at pH 7.0, 7.5 or 8.0. Some activity was measurable at 15 min at pH 6.5 and 6.0, but this fell to zero in 60 minutes. Better recovery of glucose oxidase activity was observed in deionised water.
• Example 1.2 Poor activity recovery on incubation of glucose oxidase outside of the calculated pH optimum in the presence of beneficial additives
• Tris buffer was prepared by mixing Tris base (50 mM) and lactic acid (50 mM) to achieve the required pH. There was no measurable activity following incubation of glucose oxidase at 6O 0 C for 15 minutes in the presence of TRIS/lactate at pH 7.0, 7.5, 8.0, 8.5 or 9.0. The recovery of the activity was poor in spite of the presence of beneficial additives. This is because the pH was far out from the calculated pH optimum.
• Example 1.3 Good activity recovery on incubation of glucose oxidase near the calculated pH optimum, but in the absence of beneficial additives
• citrate buffer was prepared by mixing citric acid (50 mM) with sodium hydroxide (5 M) to achieve the required pH.
• the decline of the enzyme activity was slowest at pH 4.8. Over 15% of the original activity was still measurable after 22 h incubation at 60 0 C.
• the decline of the enzyme activity was only slightly lower using the same formulations at pH 4.6 and 5.0. Nevertheless, using the same formulation with pH adjusted to >0.4 unit away from the optimum resulted in considerably faster decline of the enzyme activity.
• Example 1.4 Very good activity recovery on incubation of glucose oxidase near the calculated pH optimum in the presence of beneficial additives
• Catalase from bovine liver consists of four identical subunits (M r of each approx. 65,000). The isoelectric point of catalase is approximately 5.7. The abundance of the acid-base amino acids in each subunit is shown in Table 5
• Catalase solutions both fresh and after incubation at increased temperature, were assayed for catalase activity. This was performed according to the following procedure: 2 ml_ of hydrogen peroxide (30 mM in water) was added to 18 ml_ of PBS in a
• citrate/phosphate buffer 0.1 M, pH 5.0
• Example 2.1 Poor activity recovery on incubation of catalase outside of the calculated pH optimum both in the presence and in the absence of beneficial additives
• Citrate buffer was prepared by mixing citric acid (50 mM) with sodium hydroxide (5 M) to achieve the required pH.
• TRIS buffer was prepared by mixing Tris base (50 mM) with hydrochloric acid (5 M) to achieve required pH. There was virtually no measurable activity following incubation of catalase at 55 0 C for 60 minutes in the presence of citrate buffer at pH 4.5 or in the presence of TRIS buffer at pH 8.2. The recovery of the activity was poor because the pH was outside of the calculated pH optimum (in spite of the presence of the "beneficial additive" in the case of TRIS).
• Example 2.2 Good activity recovery on incubation of catalase near the calculated pH optimum, but in the absence of beneficial additives
• citrate buffer was prepared by mixing citric acid (50 mM) with sodium hydroxide (5 M) to achieve the required pH.
• the decline of the enzyme activity was slowest at pH 6.4. Over 20% of the original activity was still measurable after 22 h incubation at 55 0 C.
• the decline of the enzyme activity was only slightly more rapid using the same formulations at pH 6.8 and 6.0. Nevertheless, using the same formulation with pH adjusted to >0.4 unit away from the optimum resulted in considerably faster decline of the enzyme activity.
• Example 2.3 Very good activity recovery on incubation of catalase near the calculated pH optimum in the presence of beneficial additives
• Papain consists of one unit (M r of each approx. 21 ,000). The isoelectric point of papain is approximately 8.7. Papain is a protease and if activated it is capable of self-digestion. To avoid self-digestion it has to be kept in inactivated (oxidised) form. All experiments involving papain presented here were carried out using the inactive (oxidised) form of papain.
• the proton exchange frequency profile for papain is shown in Fig. 10.
• the pH optimisation algorithm gives the following results for papain:
• Example 3,1 Poor activity recovery on incubation of papain outside of the calculated pH optimum in the absence of beneficial additives
• Citrate buffer was prepared by mixing citric acid (50 mM) with sodium hydroxide (5 M) to achieve the required pH.
• TRIS buffer was prepared by mixing Tris base (50 mM) with hydrochloric acid (5 M) to achieve required pH.
• the formulation contained a positively charged protonatable group with pK a above the optimum pH (i.e. amino group of the two amino acids - pK a around 9) and a negatively charged protonatable group with pK a below the optimum pH (i.e. carboxylic groups of the tw amino acids - pK a around 3).
• the side-chain of histidine (pK a around 6) offered a convenient buffering capacity to maintain the pH at the value required.
• Glutamate dehydrogenase (from bovine liver) consists of six subunits (M r of each approx. 56,000). The isoelectric point of glutamate dehydrogenase is approximately 5.5. The abundance of the acid-base amino acids in each subunit is shown in Table 7.
• the proton exchange frequency profile for glutamate dehydrogenase is shown in Fig. 11.
• the pH optimisation algorithm gives the following results for glutamate dehydrogenase:
• Glutamate dehydrogenase solutions both fresh and after incubation at increased temperature, were assayed for glutamate dehydrogense activity. This was performed according to the following procedure:
• citrate buffer was prepared by mixing citric acid (50 mM) with sodium hydroxide (5 M) to achieve the required pH.
• TRIS buffer was prepared by mixing Tris base (50 mM) with hydrochloric acid (5 M) to achieve required pH.
• the enzyme activity dropped to about 15% (in the case of TRIS buffer, pH 8.0) and to almost zero (in the case of citrate buffer (pH 4.0) after 4 hours of incubation at 55 0 C.
• the activity fell to zero in TRIS buffer after 22 hours of incubation at the increased temperature.
• the recovery of the activity was poor because the pH was outside of the calculated pH optimum (in spite of the presence of the "beneficial additive" in the case of TRIS).
• Example 4.2 Satisfactory activity recovery on incubation of glutamate dehydrogenase near the calculated pH optimum in the presence of beneficial additives
• the formulation contained a positively charged protonatable group with pK a above the optimum pH (i.e. amino group of lysine - pK a around 9) and a negatively charged protonatable group with pK a below the optimum pH (i.e. carboxylic groups of lysine - pK a around 3). 10 mM citrate phosphate buffer was used to maintain the pH.
• Horseradish peroxidase consists of one unit (M r approx. 42,000). The commonly stated value for the most abundant isoform of peroxidase in the horseradish root is approximately 8.6. The abundance of the acid-base amino acids in the horseradish peroxidase unit is shown in Table 8.
• the first number indicates the number of cysteines that are not engaged in disulphide bond.
• the number in brackets indicates the total number of cysteines in the subunit.
• the proton exchange frequency profile for horseradish peroxidase is shown in Fig. 12.
• the pH optimisation algorithm gives the following results for horseradish peroxidase:
• Horseradish peroxidase solutions both fresh and after incubation at increased temperature, were assayed for horseradish peroxidase activity. This was performed according to the following procedure:
• citrate/phosphate buffer 0.05 M, pH 5.0
• Time 0 was counted from the addition of the horseradish peroxidase sample. Precisely after 3 min, the absorbance was then read at 630 nm. The results were expressed as percentage recovery, by reference to the absorbance measured in the samples prior to their incubation at increased temperature.
• Example 5.1 Poor activity recovery on incubation of horseradish peroxidase outside of the calculated pH optimum in the absence of beneficial additives The effect of 50 mM citrate/phosphate buffer (pH 5.0) and of phosphate buffer
• Citrate/Phosphate buffer was prepared by mixing citric acid (50 mM) with disodium hydrogen orthophosphate (50 mM) to achieve the required concentration.
• the phosphate buffer was prepared by mixing disodium hydrogen orthophosphate (50 mM) and sodium dihydrogen orthophosphate (50 mM) to achieve the required pH.
• the enzyme activity dropped to ⁇ 10% in the case of citrate/phosphate buffer (pH 5.0) and to about 30% in the case of phosphate buffer (pH 6.0) after 22 hours of incubation at 65 0 C. The recovery of the activity was poor because the pH was outside of the calculated pH optimum. There was also no positively charged protonatable functional group.
• Example 5.2 Satisfactory activity recovery on incubation of horseradish peroxidase near the calculated pH optimum in the presence of beneficial additives
• Example 6 Lactoperoxidase
• the isoelectric point of lactoperoxidase quoted in literature is 8.0-9.2. If it can be assumed that there is a structural similarity between horseradish peroxidase and lactoperoxidase (as the similar value of the isoelectric points might indicate), then the estimated pH optimum for lactoperoxidase should be similar to that for horseradish peroxidase. Lactoperoxidase solutions, both fresh and after incubation at increased temperature, were assayed for lactoperoxidase activity.
• Time 0 was counted from the addition of the lactoperoxidase sample. Precisely after 5 min, the absorbance was then read at 630 nm. The results were expressed as percentage recovery, by reference to the absorbance measured in the samples prior to their incubation at increased temperature.
• citrate/phosphate buffer pH 5.0
• phosphate buffer pH 6.0
• Citrate/Phosphate buffer was prepared by mixing citric acid (50 mM) with disodium hydrogen orthophosphate (50 mM) to achieve the required concentration.
• the phosphate buffer was prepared by mixing disodium hydrogen orthophosphate (50 mM) and sodium dihydrogen orthophosphate (50 mM) to achieve the required pH.
• the enzyme activity dropped to almost zero in the case of citrate/phosphate buffer (pH 5.0) and to about 10% in the case of phosphate buffer (pH 6.0) after 4 hours of incubation at 65 0 C.
• the recovery of the activity was poor because the pH was outside of the calculated pH optimum. There was also no positively charged protonatable functional group.
• Example 6.2 Satisfactory activity recovery on incubation of lactoperoxidase near the calculated pH optimum in the presence of beneficial additives
• Incorporation of TRIS into the lactoperoxidase formulation adjusted to the near- optimum pH resulted in satisfactory preservation of the enzyme activity on incubation at 65 0 C.
• the background solution was prepared by mixing TRIS base (50 mM) with hydrochloric acid (5 M) to achieve the required pH. 100 % of the original activity was still measurable after 4 h incubation at 65 0 C if the pH was adjusted to 7.8 or 8.2. There was only a small decline of the enzyme activity using the same formulations at pH 7.4 and 8.6.
• Uricase solutions typically 250 ⁇ g mL '1
• Uricase solutions were assayed for uricase activity. This was performed according to the following procedure: The following solutions were mixed in a 1 cm cuvette:
• borate buffer 25 mM, pH 8.5
• citrate/phosphate buffer 0.5 M, pH 4.0
• citrate/phosphate buffer 0.5 M, pH 4.0
• the resulting solution was mixed thoroughly and absorbance was read at 630 nm using a Unicam UV-visible spectrophotometer (type: Helios gamma). The results were expressed as percentage recovery, by reference to the absorbance measured in the fresh samples (i.e. prior to incubation at increased temperature).
• N is the value of the negative control AUSZYME measurement
• C1 , C2 and C3 are the values of three repeated AUSZYME measurements of the Control sample (i.e. untreated refrigerated vaccine)
• S1 , S2 and S3 are the values of three repeated AUSZYME measurements of the tested sample.
• the remaining antigenic activity of Hepatitis B vaccine was tested after incubation at 55 0 C for 2, 4 and 7 weeks.
• the stabilising formulations consisting of histidine and phosphate anion and adjusted to the optimum pH retained >95% of the original antigenic activity after 7 weeks.
• the remaining antigenic activity of the original vaccine formulation (18 mM phosphate buffer, pH 6.9-7.1, containing 132 mM sodium chloride) was ⁇ 10% at this point .
• the stabilising formulations did not appear to affect the alumina-antigen association as the antigenic activity measured in the supernatant of the stabilising formulation following centrifugation was comparable with that measured in the supernatant of the original sample. It is believed that the presence of phosphate anion ensures optimal binding of the vaccine onto the alumina.
• Example 9 Effect of polvalcohols
• Glucose oxidase was adsorbed onto alumina particles by incubation of alumina in a solution of glucose oxidase (25 ⁇ g/mL) at 4 0 C overnight.
• Citrate/Phosphate buffer 50 mM, pH 5.0
• citric acid 50 mM
• disodium hydrogen orthophosphate 50 mM
• HPLC assay was conducted as follows: Mobile phase A consisted of 0.1% TFA in water, mobile phase B consisted of 0.1% TFA in acetonitrile. The mobile phases were filtered prior to their use. Linear gradient was employed: A/B (70:30) to A/B (68:32) in 20 min.
• the liquid chromatograph (Agilent 1100 series) was equipped with a 214 nm detector and a 4.6 x 250 mm column (Zorbax Eclipse XDB-C18) 00G-4167- EO) packed with octadecylsilyl silica gel with a granulometry of 5 ⁇ m, maintained at 3O 0 C. The flow rate was maintained at 1 mL min "1 . 15 ⁇ L of aqueous samples of human insulin (typically 1-2.5 mg mL "1 ) were injected.
• a HPLC assay was conducted as follows: Mobile phase was prepared by mixing 71 parts (by volume) of a solution of TRIS (0.05 M, in water adjusted with hydrochloric acid to a pH of 7.5) and 29 parts (by volume) of n-propylalcohol. The mobile phase was filtered prior to its use.
• the liquid chromatograph (Agilent 1100 series) was equipped with a 214 nm detector and a 4.6 x 250 mm column (Phenomenex 00G-4167-E0) packed with butylsilyl silica gel with a granulometry of 5 ⁇ m and a porosity of 30 nm, maintained at 45 0 C. The flow rate was maintained at 0.5 mL min "1 . 15 ⁇ L of aqueous samples of human growth hormone (typically 1-2.5 mg mL '1 ) were injected.

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